U.S. patent number 7,239,110 [Application Number 11/000,030] was granted by the patent office on 2007-07-03 for primary units, methods and systems for contact-less power transfer.
This patent grant is currently assigned to Splashpower Limited. Invention is credited to Pilgrim Giles William Beart, Lily Ka-Lai Cheng, James Westwood Hay.
United States Patent |
7,239,110 |
Cheng , et al. |
July 3, 2007 |
Primary units, methods and systems for contact-less power
transfer
Abstract
There is disclosed a system and method for transferring power
without requiring direct electrical conductive contacts. There is
provided a primary unit having a power supply and a substantially
laminar charging surface having at least one conductor that
generates an electromagnetic field when a current flows
therethrough and having an charging area defined within a perimeter
of the surface, the at least one conductor being arranged such that
electromagnetic field lines generated by the at least one conductor
are substantially parallel to the plane of the surface or at least
subtend an angle of 45.degree. or less to the surface within the
charging area; and at least one secondary device including at least
one conductor that may be wound about a core. Because the
electromagnetic field is spread over the charging area and is
generally parallel or near-parallel thereto, coupling with flat
secondary devices such as mobile telephones and the like is
significantly improved in various orientations thereof.
Inventors: |
Cheng; Lily Ka-Lai (London,
GB), Hay; James Westwood (Cambridge, GB),
Beart; Pilgrim Giles William (Harston, GB) |
Assignee: |
Splashpower Limited
(GB)
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Family
ID: |
34682368 |
Appl.
No.: |
11/000,030 |
Filed: |
December 1, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050135122 A1 |
Jun 23, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10514046 |
Feb 28, 2005 |
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Foreign Application Priority Data
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May 13, 2002 [GB] |
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0210886.8 |
Jun 7, 2002 [GB] |
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0213024.3 |
Oct 28, 2002 [GB] |
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0225006.6 |
Dec 6, 2002 [GB] |
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0228425.5 |
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Current U.S.
Class: |
320/108 |
Current CPC
Class: |
H02J
50/70 (20160201); H02J 50/12 (20160201); H02J
50/40 (20160201); H02J 50/402 (20200101); H02J
7/025 (20130101); H02J 7/0042 (20130101) |
Current International
Class: |
H01M
10/46 (20060101) |
Field of
Search: |
;320/108,112,114,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tso; Edward H.
Attorney, Agent or Firm: Stites & Harbison PLLC Hunt,
Jr.; Ross F.
Parent Case Text
This application is a divisional of application Ser. No.
10/514,046, filed on Feb. 28, 2005, which claims priority from UK
patent applications nos 0210886.8 of 13 May 2002, 0213024.3 of 7
Jun. 2002, 0225006.6 of 28 Oct. 2002 and 0228425.5 of 6 Dec. 2002,
as well as from U.S. patent application Ser. No. 10/326,571 of 20
Dec. 2002. The full contents of all of these prior patent
application is hereby incorporated into the present application by
reference.
Claims
The invention claimed is:
1. A primary unit having a power transfer area in or over which a
secondary device, separable from the primary unit, can be placed in
a stationary working disposition to receive power from the primary
unit without requiring direct electrical conductive contacts
between the primary unit and the secondary device, the primary unit
comprising: first and second field generators, each arranged
substantially in parallel with said power transfer area and each
configured so that if driven individually the generator generates
an electromagnetic field having field lines which extend generally
in a predetermined direction across at least part of said power
transfer area and which have significant resolved components
parallel to the power transfer area, said predetermined direction
of said first field generator being different from said
predetermined direction of said second field generator; and a
driving unit for applying electrical drive signals to said first
and second field generators such that the first and second field
generators cooperate to generate, in or over said at least one part
of the power transfer area, field lines which, when resolved onto
the power transfer area, change in direction over time.
2. A primary unit as claimed in claim 1, wherein said driving unit
is operable to apply electrical drive signals to said first and
second field generators such that said field lines are switched
between two or more different predetermined directions over
time.
3. A primary unit as claimed in claim 1, wherein the driving unit
is operable to apply electrical drive signals to said first and
second field generators such that the field line directions are
rotated through an angle over time.
4. A primary unit as claimed in claim 1, wherein said driving unit
is operable to apply electrical drive signals to said first and
second field generators such that the field line directions are
rotated through a complete circle over time.
5. A primary unit as claimed in claim 1, wherein: said first field
generator comprises at least one first conductive element; said
second field generator comprises at least one second conductive
element; and said first conductive element(s) extend(s)
substantially perpendicularly to said second conductive
element(s).
6. A primary unit as claimed in claim 5, wherein: said first and
second conductive elements are arranged in a generating area in or
generally parallel to said power transfer area; and the first and
second conductive elements are shaped and arranged such that, at
each crosspoint where a first conductive element extends across a
second conductive element, the first and second conductive elements
extend in mutually orthogonal directions.
7. A primary unit as claimed in claim 6, wherein said first field
generator comprises a plurality of first conductive elements
extending generally in parallel with one another and generally in a
direction perpendicular to said first direction, and said second
field generator comprises a plurality of second conductive elements
extending generally in parallel with one another and generally in a
direction perpendicular to said second direction.
8. A primary unit as claimed in claim 7, wherein the driving unit
is operable to cause currents to flow in the same direction
simultaneously through all of said first conductive elements and to
cause currents to flow in the same direction simultaneously through
all of the second conductive elements.
9. primary unit as claimed in claim 5, further comprising a
magnetic core across which the first and second conductive elements
extend.
10. A primary unit as claimed in claim 5, wherein each said first
conductive element and/or each said second conductive element is
straight.
11. A primary unit as claimed in claim 5, wherein each said first
conductive element is not straight and/or each second conductive
element is not straight.
12. A primary unit as claimed in claim 5, wherein each said first
conductive element is in the form of a loop and each said second
conductive element extends transversely across at least one said
first conductive element at a different position around the
loop.
13. A primary unit as claimed in claim 12, wherein at least one
said second conductive element extends transversely across two or
more different first conductive elements.
14. A primary unit as claimed in claim 12, wherein said loop is a
generally circular loop and said second conductive elements extend
radially across the circular first conductive elements at different
positions therearound.
15. A primary unit as claimed in claim 12, wherein said loop is an
irregular loop and each said second conductive element is locally
substantially perpendicular to each first conductive element.
16. A primary unit as claimed in claim 5, having at least first and
second coils, said first conductive elements being provided by
different parts of said first coil and said second conductive
elements being provided by different parts of said second coil.
17. A primary unit as claimed in claim 16, wherein said first coil
has a generally flat spiral shape and said second coil is wound in
a toroidal form through the centre of the first coil and out to the
perimeter thereof in a radial fashion.
18. A primary unit as claimed in claim 5, wherein the first
conductive elements and the second conductive elements are
conductive tracks formed on one or more planar surfaces.
19. A primary unit as claimed in claim 5, wherein said driving unit
is operable to apply electrical drive signals to the first and
second field generators alternately.
20. A primary unit as claimed in claim 5, wherein said driving unit
is operable to apply electrical drive signals in quadrature to the
first and second field generators.
21. A primary unit as claimed in claim 1, wherein at any given time
said field lines are substantially parallel to one another over
said power transfer area.
22. A primary unit as claimed in claim 1, wherein said field lines
are generally parallel to said power transfer surface within said
power transfer area.
23. A method of transferring power from a primary unit to a
secondary device, separable from the primary unit, without
requiring direct electrical conductive contacts between the primary
unit and the secondary device, the method comprising: employing
first and second field generators to generate an electromagnetic
field across a power transfer area in or over which the secondary
device is placed in a stationary working disposition to receive
power from the primary unit, each of said first and second field
generators means being arranged substantially in parallel with said
power transfer area and each being configured so that if driven
individually the generator generates an electromagnetic field
having field lines which extend generally in a predetermined
direction across at least part of said power transfer area and
which have significant resolved components parallel to the power
transfer area, said predetermined direction of said first field
generator being different from said predetermined direction of said
second field generator; and applying electrical drive signals to
said first and second field generators such that the first and
second field generators cooperate to generate, in or over said at
least one part of the power transfer area, field lines which, when
resolved onto the power transfer area, change in direction over
time.
24. A system for transferring power without requiring direct
electrical conductive contacts, the system comprising: a
substantially flat power transfer surface; a primary unit having a
field generator arranged at or beneath said power transfer surface
for generating an electromagnetic field distributed over a
predetermined power transfer area of the surface; and two or more
objects to be powered, physically and electrically separate from
one another and each separable from the primary unit and each
carrying a secondary device adapted to receive power inductively
from the primary unit when the object is placed on the power
transfer surface so that the object is lying across the surface;
wherein said field generated by said field generator is such that
the secondary device of each said object can receive power
inductively from the primary unit when the object is placed
anywhere within said power transfer area; the power transfer area
is of sufficient size that the two or more objects can be placed at
different respective positions within the power transfer area to
enable their respective secondary devices to receive power
simultaneously from the primary unit; and there being no
substantial discontinuities in the power transfer area, at which
one of said objects cannot be placed to receive power, from one
side of the area to the other in two dimensions.
25. A system as claimed in claim 24, wherein there are no
substantial discontinuities in the power transfer area, where one
of said objects cannot be placed to receive power, from one side of
the area to the other in two dimensions.
26. A system as claimed in claim 24, wherein field lines of said
field are substantially parallel to one another at any given moment
in time over said power transfer area.
27. A system as claimed in claim 24, wherein field lines of said
field are generally parallel to said power transfer surface at
least over a central part of said power transfer area.
28. A system as claimed in claim 24, wherein said primary unit
comprises a sensing unit which senses one or more of the following:
(a) the presence at the primary unit of a secondary device; (b) the
number of secondary devices present at said primary unit; and (c)
the presence at said primary unit of magnetic material which is not
part of one of the secondary devices of the system.
29. A system as claimed in claim 28, wherein the primary unit
comprises a control unit which is connected operatively to the said
sensing unit and which controls a current supplied to the field
generator in dependence upon the sensing result(s).
30. A system as claimed in claim 28, wherein the primary unit
comprises a visual indicator which indicates the presence at the
primary unit of a secondary device.
31. A system as claimed in claim 28, wherein the primary unit
comprises a visual indicator which indicates the number of
secondary devices present at said primary unit.
32. system as claimed in claim 24, wherein said field generator
comprises a resonant circuit, and the primary unit further
comprises a control unit operable to maintain operation of said
resonant circuit at or near resonance as the number of secondary
devices present at said primary unit changes.
33. A system as claimed in claim 32, wherein said control unit is
operable to change an operating frequency of said resonant circuit
so as to maintain said operation at or near resonance as the number
of secondary devices present at the primary unit changes.
34. A system as claimed in claim 32, wherein said control unit is
operable to change a capacitance of said resonant circuit so as to
maintain said operation at or near resonance as the number of
secondary devices present at said primary unit changes.
35. A system as claimed in claim 34, wherein said secondary devices
are designed such that placing each additional device lying across
the power transfer surface of the primary unit changes an
inductance of said resonance circuit to a different one of a
plurality of predetermined inductance values, and said control unit
is operable to change the capacitance of said resonant circuit to
one of a plurality of predetermined capacitance values suitable for
maintaining said operation at or near resonance when the inductance
has a corresponding one of said plurality of predetermined
inductance values.
36. A system as claimed in claim 34, wherein said control unit has
a set of capacitance elements which can be selectively switched in
or out of said resonant circuit to change said capacitance
thereof.
37. system as claimed in claim 32, wherein said resonant circuit is
configured such that it is detuned automatically when no such
secondary device is present at the primary unit.
38. A system as claimed in claim 24, wherein two or more secondary
devices have the same standard size.
39. A system as claimed in claim 24, wherein at least one said
secondary device is carried in or by a rechargeable battery or cell
fitted, or adapted to be fitted, into an object requiring
power.
40. A system as claimed in claim 39, wherein, when said battery or
cell is fitted into said object and said object is placed lying
across said power transfer surface, the battery or cell can be
recharged without removing it from said object.
41. A system as claimed in claim 24, wherein at least one said
object is a portable electrical or electronic device.
42. A system as claimed in claim 24, wherein at least one said
object is a mobile communication device.
43. A system as claimed in claim 24, wherein one such object
carrying one said secondary device has a power requirement
different from that of another such object carrying another one of
said secondary devices.
44. A primary unit for use in a power transfer system having a
power transfer surface shaped and arranged such that a secondary
device, separable from the primary unit, can be placed on or in
proximity to the surface to receive power from the primary unit
without requiring direct electrical conductive contacts between the
primary unit and the secondary device, which primary unit
comprises: a field generator arranged at or parallel to the power
transfer surface for generating an electromagnetic field over a
power transfer area of the surface, said power transfer area being
larger than an area of the surface covered by the secondary device,
and the field being distributed over the power transfer area such
that a secondary device can receive power from the primary unit
when placed at any lateral position across the area, at least in
one rotational orientation of the secondary device about an axis
perpendicular to the surface; and wherein said field generator
comprises one or more conductive elements for generating flux and
also comprises one or more elements made of magnetic material
arranged to couple with the flux generated by the conductive
element(s) and distribute the flux parallel to the power transfer
surface, said conductive element(s) and said element(s) of magnetic
material being shaped and arranged with respect to said power
transfer area such that an instantaneous field strength of said
electromagnetic field, measured in said rotational orientation and
at a given distance from the surface, is substantially the same at
each said lateral position across the area.
45. A primary unit as claimed in claim 44, wherein field lines of
said electromagnetic field have significant resolved components
parallel to said power transfer surface within said power transfer
area.
46. A primary unit as claimed in claim 44, wherein there are no
substantial discontinuities in said power transfer area, where the
secondary device cannot be placed to receive power, from one side
of the area to the other in two dimensions.
47. A primary unit as claimed in claim 44, wherein said field
generator comprises a plurality of substantially coplanar
conductive elements arranged at or beneath said power transfer
surface in a generating area, for generating said electromagnetic
field over said power transfer area.
48. A primary unit as claimed in claim 47, wherein said
substantially coplanar conductive elements extend generally in
parallel with one another across said generating area, and the
respective instantaneous currents which flow simultaneously through
all the conductive elements in said generating area have the same
general direction.
49. A primary unit as claimed in claim 47, wherein said conductive
elements in said generating area are substantially straight.
50. A primary unit as claimed in claim 47, wherein at least one
pair of adjacent conductive elements has a mutual spacing different
from that of another pair of adjacent conductive elements.
51. A primary unit as claimed in claim 47, further comprising a
magnetic core across which the conductive elements extend.
52. A primary unit as claimed in claim 47, wherein two or more of
the plurality of conductive elements are different parts of the
same coil.
53. A primary unit as claimed in claim 52, wherein said coil is
wound about a magnetic core.
54. A primary unit as claimed in claim 47, having further
conductive elements outside said generating area which are
connected with said conductive elements within the generating area,
the currents flowing through said further conductive elements being
generally in the opposite direction to the direction through which
currents flow through the conductive elements in said generating
area, and the system further comprising magnetic material arranged
over the further conductive elements for shielding the effects
thereof.
55. A primary unit as claimed in claim 47, wherein the plurality of
conductive elements are conductive tracks formed on a planar
surface.
56. A primary unit as claimed in claim 47, having first and second
spiral conductors arranged side by side, each with parts in the
generating area, the current in one of the first and second spiral
conductors flowing in an anticlockwise direction at a given moment
in time and the current in the other one of the first and second
spiral conductors flowing in a clockwise direction at the same
moment in time and the plurality of conductive elements comprising
first conductive elements provided by different sections of the
first spiral conductor and second conductive elements provided by
different sections of the second spiral conductor.
57. A primary unit as claimed in claim 47, having first and second
such generating areas arranged side by side, the plurality of
conductive elements comprising first conductive elements in said
first generating area and second conductive elements in said second
generating area, and also having a spiral conductor with first
sections in said first generating area which provide said first
conductive elements and with second sections in said second
generating area which provide said second conductive elements,
whereby an instantaneous current flowing through said spiral
conductor flows through each of said first conductive elements in
one direction and through each of said second conductive elements
in the opposite direction.
58. A primary unit as claimed in claim 44, wherein said element(s)
of magnetic material extend(s) at least partially around a
perimeter of the power transfer and the conductive elements are
arranged to generate first and second fluxes which are guided by
the element(s) of magnetic material to propagate in respective
opposite directions around said perimeter.
59. A primary unit as claimed in claim 58, having a single element
of magnetic material which extends continuously around said
perimeter.
60. A primary unit as claimed in claim 58, having two said elements
of magnetic material that are opposed to one another and are
horseshoe-shaped.
61. A primary unit as claimed in claim 58, wherein the conductive
elements form part of first and second coils arranged on opposite
sides respectively of the power transfer area.
62. A primary unit as claimed in claim 61, wherein each said coil
is wound around the or one of said element(s) of magnetic
material.
63. A system for transferring power without requiring direct
electrical conductive contacts, the system comprising: a power
transfer surface shaped and arranged such that a secondary device
can be placed on or in proximity to the surface to receive power
when the system is in use; a primary unit having a field generator,
arranged at or parallel to the power transfer surface, which
generates an electromagnetic field over a power transfer area of
the surface, said power transfer area being larger than an area of
the surface covered by the secondary device, and the field being
distributed over the power transfer area such that a secondary
device can receive power from the primary unit when placed at any
lateral position across the area, at least in one rotational
orientation of the secondary device about an axis perpendicular to
the surface; and a secondary device separable from the primary unit
and including at least one electrical conductor with which the
electromagnetic field generated by the field generator couples and
induces a current to flow in the conductor when the secondary
device is placed in said at least one rotational orientation at any
said lateral position; wherein said field generator comprises one
or more conductive elements which generate flux and also comprises
one or more elements made of magnetic material arranged to couple
with the flux generated by the conductive element(s) and distribute
the flux parallel to the power transfer surface, said conductive
element(s) and said element(s) of magnetic material being shaped
and arranged with respect to said power transfer area such that an
instantaneous field strength of said electromagnetic field,
measured in said rotational orientation and at a given distance
from the surface, is substantially the same at each said lateral
position across the area.
64. A system as claimed in claim 63, wherein said secondary device
comprises a coil which provides said at least one electrical
conductor and which is arranged such that a central axis of the
coil extends in a predetermined working direction when the
secondary device is placed in said rotational orientation, and a
field strength of said electromagnetic field, measured parallel to
said working direction and at said given distance, is substantially
uniform in magnitude at each said lateral position across the power
transfer area.
65. system as claimed in claim 64, wherein said working direction
is substantially non-perpendicular to said power transfer surface
at least within said power transfer area.
66. A system as claimed in claim 63, wherein said secondary device
comprises a flux-concentrating core about which said at least one
electrical conductor is wound, said core being arranged such that a
longitudinal axis thereof extends in a working direction when the
secondary device is placed in said rotational orientation, and a
field strength of said electromagnetic field, measured parallel to
said working direction and at said given distance, is substantially
uniform in magnitude at each said lateral position across the power
transfer area.
67. A system as claimed in claim 66, wherein said working direction
is substantially non-perpendicular to said power transfer surface
at least within said power transfer area.
68. A system as claimed in claim 63, wherein said secondary device
is carried in or by an object requiring power and can receive power
from the primary unit when said object is placed on or in proximity
to said power transfer surface so that the carried secondary device
has its said rotational orientation.
69. A system as claimed in claim 63, wherein said secondary device
is carried in or by a rechargeable battery or cell fitted, or
adapted to be fitted, into an object requiring power.
70. A system as claimed in claim 69, wherein, when said battery or
cell is fitted into said object and said object is placed on or in
proximity to said power transfer surface so that said secondary
device has its said rotational orientation, the battery or cell can
be recharged without removing it from said object.
71. A primary unit having a power transfer area in or over which a
secondary device, separable from the primary unit, can be placed in
a stationary working disposition to receive power from the primary
unit without requiring direct electrical conductive contacts
between the primary unit and the secondary device, the primary unit
comprising: first and second field generating means, each arranged
substantially in parallel with said power transfer area and each
configured so that if driven individually the field generating
means generates an electromagnetic field having field lines which
extend generally in a predetermined direction across at least part
of said power transfer area and which have significant resolved
components parallel to the power transfer area, said predetermined
direction of said first field generating means being different from
said predetermined direction of said second field generating means;
and driving means for applying electrical drive signals to said
first and second field generating means such that the first and
second field generating means cooperate to generate, in or over
said at least one part of the power transfer area, field lines
which, when resolved onto the power transfer area, change in
direction over time.
72. A system for transferring power without requiring direct
electrical conductive contacts, the system comprising: a
substantially flat power transfer surface; a primary unit having
field generating means arranged at or beneath said power transfer
surface for generating an electromagnetic field distributed over a
predetermined power transfer area of the surface; and two or more
objects to be powered, physically and electrically separate from
one another and each separable from the primary unit and each
carrying a secondary device adapted to receive power inductively
from the primary unit when the object is placed on the power
transfer surface so that the object is lying across the surface;
wherein said field generated by said field generating means is such
that the secondary device of each said object can receive power
inductively from the primary unit when the object is placed
anywhere within said power transfer area; the power transfer area
is of sufficient size that the two or more objects can be placed at
different respective positions within the power transfer area to
enable their respective secondary devices to receive power
simultaneously from the primary unit; and there being no
substantial discontinuities in the power transfer area, at which
one of said objects cannot be placed to receive power, from one
side of the area to the other in two dimensions.
73. A primary unit for use in a power transfer system having a
power transfer surface shaped and arranged such that a secondary
device, separable from the primary unit, can be placed on or in
proximity to the surface to receive power from the primary unit
without requiring direct electrical conductive contacts between the
primary unit and the secondary device, which primary unit
comprises: field generating means arranged at or parallel to the
power transfer surface for generating an electromagnetic field over
a power transfer area of the surface, said power transfer area
being larger than an area of the surface covered by the secondary
device, and the field being distributed over the power transfer
area such that a secondary device can receive power from the
primary unit when placed at any lateral position across the area,
at least in one rotational orientation of the secondary device
about an axis perpendicular to the surface; and wherein said field
generating means comprises one or more conductive elements for
generating flux and also comprises one or more elements made of
magnetic material arranged to couple with the flux generated by the
conductive element(s) and distribute the flux parallel to the power
transfer surface, said conductive element(s) and said element(s) of
magnetic material being shaped and arranged with respect to said
power element(s) of magnetic material being shaped and arranged
with respect to said power transfer area such that an instantaneous
field strength of said electromagnetic field, measured in said
rotational orientation and at a given distance from the surface, is
substantially the same at each said lateral position across the
area.
74. A primary unit as claimed in claim 44, wherein substantially
all of the conductive elements within the power transfer area form
part of the same coil.
75. A primary unit for transferring power to at least one secondary
device without requiring direct electrical conductive contacts, the
or each secondary device being separable from the primary unit,
which primary unit comprises: a power transfer surface shaped and
arranged such that a secondary device can be placed on or in
proximity to the surface to receive power when the primary unit is
in use; and a field generator arranged at or parallel to the power
transfer surface for generating an electromagnetic field over a
power transfer area of the surface, said power transfer area being
larger than an area of the surface covered by the secondary device,
and the field being distributed over the power transfer area such
that a secondary device can receive power from the primary unit
when placed, in at least one rotational orientation of the
secondary device about an axis perpendicular to the surface, on the
surface at any position within the power transfer area or in
proximity to the surface along a normal to the surface that passes
through any such position within the power transfer area; wherein
said field generator comprises at least one conductive element for
generating flux and also comprises magnetic material arranged at or
beneath substantially the whole of the power transfer area for
coupling with the flux generated by the at least one conductive
element and distributing the flux parallel to the power transfer
surface, such that a field strength of said electromagnetic field,
measured at the surface or at a given distance therefrom and in a
predetermined working direction applicable to the position
concerned, is substantially uniform in magnitude at substantially
all said positions within the power transfer area.
Description
This invention relates to a new apparatus and method for
transferring power in a contact-less fashion.
Many of today's portable devices incorporate "secondary" power
cells which can be recharged, saving the user the cost and
inconvenience of regularly having to purchase new cells. Example
devices include cellular telephones, laptop computers, the Palm 500
series of Personal Digital Assistants, electric shavers and
electric toothbrushes. In some of these devices, the cells are
recharged via inductive coupling rather than direct electrical
connection. Examples include the Braun Oral B Plak Control power
toothbrush, the Panasonic Digital Cordless Phone Solution KX-PH15AL
and the Panasonic multi-head men's shavers ES70/40 series.
Each of these devices typically has an adaptor or charger which
takes power from mains electricity, a car cigarette lighter or
other sources of power and converts it into a form suitable for
charging the secondary cells. There are a number of problems
associated with conventional means of powering or charging these
devices: Both the characteristics of the cells within each device
and the means of connecting to them vary considerably from
manufacturer to manufacturer, and from device to device. Therefore
users who own several such devices must also own several different
adaptors. If users are going away on travel, they will have to
bring their collection of chargers if they expect to use their
devices during this time. These adaptors and chargers often require
users to plug a small connector into the device or to place the
device with accurate alignment into a stand causing inconvenience.
If users fail to plug or place their device into a charger and it
runs out of power, the device becomes useless and important data
stored locally in the device might even be lost. In addition, most
adaptors and chargers have to be plugged into mains sockets and
hence if several are used together, they take up space in plug
strips and create a messy and confusing tangle of wires. Besides
the above problems with conventional methods of recharging devices,
there are also practical problems associated with devices having an
open electrical contact. For example, devices cannot be used in wet
environments due to the possibility of corroding or shorting out
the contacts and also they cannot be used in flammable gaseous
environments due to the possibility of creating electrical
sparks.
Chargers which use inductive charging remove the need to have open
electrical contacts hence allowing the adaptor and device to be
sealed and used in wet environments (for example the electric
toothbrush as mentioned above is designed to be used in a
bathroom). However such chargers still suffer from all other
problems as described above. For example, the devices still need to
be placed accurately into a charger such that the device and the
charger are in a predefined relative position (See FIGS. 1a and
1b). The adaptors are still only designed specifically for a
certain make and model of device and are still only capable of
charging one device at a time. As a result, users still need to
possess and manage a collection of different adaptors.
Universal chargers (such as the Maha MH-C777 Plus Universal
charger) also exist such that battery packs of different shapes and
characteristics can be removed from the device and charged using a
single device. Whilst these universal chargers eliminate the need
for having different chargers for different devices, they create
even more inconvenience for the user in the sense that the battery
packs first need to be removed, then the charger needs to be
adjusted and the battery pack needs to be accurately positioned in
or relative to the charger. In addition, time must be spent to
determine the correct pair of battery pack metal contacts which the
charger must use.
It is known from U.S. Pat. No. 3,938,018 "Induction charging
system" to provide a means for non-contact battery charging whereby
an inductive coil on the primary side aligns with a horizontal
inductive coil on a secondary device when the device is placed into
a cavity on the primary side. The cavity ensures the relatively
precise alignment which is necessary with this design to ensure
that good coupling is achieved between the primary and secondary
coils.
It is also known from U.S. Pat. No. 5,959,433 "Universal Inductive
Battery Charger System" to provide a non-contact battery charging
system. The battery charger described includes a single charging
coil which creates magnetic flux lines which will induce an
electrical current in a battery pack which may belong to cellular
phones or laptop computers.
It is also known from U.S. Pat. No. 4,873,677 "Charging Apparatus
for an Electronic Device" to provide an apparatus for charging an
electronic device which includes a pair of coils. This pair of
coils is designed to operate in anti-phase such that magnetic flux
lines are coupled from one coil to the other. An electronic device
such as a watch can be placed on these two coils to receive
power.
It is also known from U.S. Pat. No. 5,952,814 "Induction charging
apparatus and an electronic device" to provide an induction charger
for charging a rechargeable battery. The shape of the external
casing of the electronic device matches the internal shape of the
charger thus allowing for accurate alignment of the primary and
secondary coils.
It is also known from U.S. Pat. No. 6,208,115 "Battery substitute
pack" to provide a substitute battery pack which may be inductively
recharged.
It is known from WO 00/61400 "Device for Inductively Transmitting
Electrical Power" to provide a means of transferring power
inductively to conveyors.
It is known from WO 95/11545 "Inductive power pick-up coils" to
provide a system for inductive powering of electric vehicles from a
series of in-road flat primaries.
To overcome the limitations of inductive power transfer systems
which require that secondary devices be axially aligned with the
primary unit, one might propose that an obvious solution is to use
a simple inductive power transfer system whereby the primary unit
is capable of emitting an electromagnetic field over a large area
(See FIG. 2a). Users can simply place one or more devices to be
recharged within range of the primary unit, with no requirement to
place them accurately. For example this primary unit may consist of
a coil encircling a large area. When a current flows through the
coil, an electromagnetic field extending over a large area is
created and devices can be placed anywhere within this area.
Although theoretically feasible, this method suffers from a number
of drawbacks. Firstly, the intensity of electromagnetic emissions
is governed by regulatory limits. This means that this method can
only support power transfer at a limited rate. In addition, there
are many objects that can be affected by the presence of an intense
magnetic field. For example, data stored on credit cards maybe
destroyed and objects made of metal will have induced therein eddy
currents generating undesired heating effects. In addition, if a
secondary device comprising a conventional coil (see FIG. 2a) is
placed against a metallic plate such as a copper plane in a printed
circuit board or metallic can of a cell, coupling is likely to be
significantly reduced.
To avoid the generation of large magnetic fields, one might suggest
using an array of coils (See FIG. 3) whereby only the coils needed
are activated. This method is described in a paper published in the
Journal of the Magnetics Society of Japan titled "Coil Shape in a
Desk-type Contactless Power Station System" (29 Nov. 2001). In an
embodiment of the multiple-coil concept, a sensing mechanism senses
the relative location of the secondary device relative to the
primary unit. A control system then activates the appropriate coils
to deliver power to the secondary device in a localised fashion.
Although this method provides a solution to the problems previously
listed, it does so in a complicated and costly way. The degree to
which the primary field can be localised is limited by the number
of coils and hence the number of driving circuits used (i.e. the
"resolution" of the primary unit). The cost associated with a
multiple-coil system would severely limit the commercial
applications of this concept. Non-uniform field distribution is
also a drawback. When all the coils are activated in the primary
unit, they sum to an equivalent of a large coil, the magnetic field
distribution of which is seen to exhibit a minimum at the centre of
the coil.
Another scheme is outlined in U.S. Pat. No. 5,519,262 "Near Field
Power Coupling System", whereby a primary unit has a number of
narrow inductive coils (or alternatively capacitive plates)
arranged from one end to the other of a flat plate, creating a
number of vertical fields which are driven in a phase-shifted
manner so that a sinusoidal wave of activity moves across the
plate. A receiving device has two vertical field pickups arranged
so that regardless of its position on the plate it can always
collect power from at least one pickup. While this scheme also
offers freedom of movement of the device, it has the disadvantages
of needing a complex secondary device, having a fixed resolution,
and having poor coupling because the return flux path is through
air.
None of the prior art solutions can satisfactorily address all of
the problems that have been described. It would be convenient to
have a solution which is capable of transferring power to portable
devices with all of the following features and is cost effective to
implement: Universality: a single primary unit which can supply
power to different secondary devices with different power
requirements thereby eliminating the need for a collection of
different adaptors and chargers; Convenience: a single primary unit
which allows secondary devices to be placed anywhere within an
active vicinity thereby eliminating the need for plugging-in or
placing secondary devices accurately relative to an adaptor or
charger; Multiple-load: a single primary unit that can supply power
to a number of secondary different devices with different power
requirements at the same time; Flexibility for use in different
environments: a single primary unit that can supply power to
secondary devices such that no direct electrical contact is
required thereby allowing for secondary devices and the primary
unit itself to be used in wet, gaseous, clean and other atypical
environments; Low electromagnetic emissions: a primary unit that
can deliver power in a manner that will minimize the intensity and
size of the magnetic field generated.
It is further to be appreciated that portable appliances are
proliferating and they all need batteries to power them. Primary
cells, or batteries of them, must be disposed of once used, which
is expensive and environmentally unfriendly. Secondary cells or
batteries can be recharged and used again and again.
Many portable devices have receptacles for cells of an
industry-standard size and voltage, such as AA, AAA, C, D and PP3.
This leaves the user free to choose whether to use primary or
secondary cells, and of various types. Once depleted, secondary
cells must typically be removed from the device and placed into a
separate recharging unit. Alternatively, some portable devices do
have recharging circuitry built-in, allowing cells to be recharged
in-situ once the device is plugged-in to an external source of
power.
It is inconvenient for the user to have to either remove cells from
the device for recharging, or to have to plug the device into an
external power source for recharging in-situ. It would be far
preferable to be able to recharge the cells without doing either,
by some non-contact means.
Some portable devices are capable of receiving power coupled
inductively from a recharger, for example the Braun Oral B Plak
Control toothbrush. Such portable devices typically have a custom,
dedicated power-receiving module built-in to the device, which then
interfaces with an internal standard cell or battery (which may or
may not be removable).
However it would be convenient if the user could transform any
portable device which accepts industry-standard cell sizes into an
inductively-rechargeable device, simply by fitting
inductively-rechargeable cells or batteries, which could then be
recharged in-situ by placing the device onto an inductive
recharger.
Examples of prior art include U.S. Pat. No. 6,208,115, which
discloses a substitute battery pack which may be inductively
recharged.
According to a first aspect of the present invention, there is
provided a system for transferring power without requiring direct
electrical conductive contacts, the system comprising: i) a primary
unit including a substantially laminar charging surface and at
least one means for generating an electromagnetic field, the means
being distributed in two dimensions across a predetermined area in
or parallel to the charging surface so as to define at least one
charging area of the charging surface that is substantially
coextensive with the predetermined area, the charging area having a
width and a length on the charging surface, wherein the means is
configured such that, when a predetermined current is supplied
thereto and the primary unit is effectively in electromagnetic
isolation, an electromagnetic field generated by the means has
electromagnetic field lines that, when averaged over any quarter
length part of the charging area measured parallel to a direction
of the field lines, subtend an angle of 45.degree. or less to the
charging surface in proximity thereto and are distributed in two
dimensions thereover, and wherein the means has a height measured
substantially perpendicular to the charging area that is less than
either of the width or the length of the charging area; and ii) at
least one secondary device including at least one electrical
conductor; wherein, when the at least one secondary device is
placed on or in proximity to a charging area of the primary unit,
the electromagnetic field lines couple with the at least one
conductor of the at least one secondary device and induce a current
to flow therein.
According to a second aspect of the present invention, there is
provided a primary unit for transferring power without requiring
direct electrical conductive contacts, the primary unit including a
substantially laminar charging surface and at least one means for
generating an electromagnetic field, the means being distributed in
two dimensions across a predetermined area in or parallel to the
charging surface so as to define at least one charging area of the
charging surface that is substantially coextensive with the
predetermined area, the charging area having a width and a length
on the charging surface, wherein the means is configured such that,
when a predetermined current is supplied thereto and the primary
unit is effectively in electromagnetic isolation, an
electromagnetic field generated by the means has electromagnetic
field lines that, when averaged over any quarter length part of the
charging area measured parallel to a direction of the field lines,
subtend an angle of 45.degree. or less to the charging surface in
proximity thereto and are distributed in two dimensions thereover,
and wherein the means has a height measured substantially
perpendicular to the charging area that is less than either of the
width or the length of the charging area.
According to a third aspect of the present invention, there is
provided a method of transferring power in a non-conductive manner
from a primary unit to a secondary device, the primary unit
including a substantially laminar charging surface and at least one
means for generating an electromagnetic field, the means being
distributed in two dimensions across a predetermined area in or
parallel to the charging surface so as to define at least one
charging area of the charging surface that is substantially
coextensive with the predetermined area, the charging area having a
width and a length on the charging surface, the means having a
height measured substantially perpendicular to the charging area
that is less than either of the width or the length of the charging
area, and the secondary device having at least one electrical
conductor; wherein: i) an electromagnetic field, generated by the
means when energised with a predetermined current and measured when
the primary unit is effectively in electromagnetic isolation, has
electromagnetic field lines that, when averaged over any quarter
length part of the charging area measured parallel to a direction
of the field lines, subtend an angle of 45.degree. or less to the
charging surface in proximity thereto and are distributed in two
dimensions over the at least one charging area when averaged
thereover; and ii) the electromagnetic field links with the
conductor of the secondary device when this is placed on or in
proximity to the charging area.
According to a fourth aspect of the present invention, there is
provided a secondary device for use with the system, unit or method
of the first, second or third aspects, the secondary device
including at least one electrical conductor and having a
substantially laminar form factor.
In the context of the present application, the word "laminar"
defines a geometry in the form of a thin sheet or lamina. The thin
sheet or lamina may be substantially flat, or may be curved.
The primary unit may include an integral power supply for the at
least one means for generating an electromagnetic field, or may be
provided with connectors or the like enabling the at least one
means to be connected to an external power supply.
In some embodiments, the means for generating the electromagnetic
field have a height that is no more than half the width or half the
length of the charging area; in some embodiments, the height may be
no more than 1/5 of the width or 1/5 of the length of the charging
area.
The at least one electrical conductor in the secondary device may
be wound about a core that serves to concentrate flux therein. In
particular, the core (where provided) may offer a path of least
resistance to flux lines of the electromagnetic field generated by
the primary unit. The core may be amorphous magnetically permeable
material. In some embodiments, there is no need for an amorphous
core.
Where an amorphous core is provided, it is preferred that the
amorphous magnetic material is a non-annealed or substantially
as-cast state. The material may be at least 70% non-annealed, or
preferably at least 90% non-annealed. This is because annealing
tends to make amorphous magnetic materials brittle, which is
disadvantageous when contained in a device, such as a mobile phone,
which may be subjected to rough treatment, for example by being
accidentally dropped. In a particularly preferred embodiment, the
amorphous magnetic material is provided in the form of a flexible
ribbon, which may comprise one or more layers of one or more of the
same or different amorphous magnetic materials. Suitable materials
include alloys which may contain iron, boron and silicon or other
suitable materials. The alloy is melted and then cooled so rapidly
("quenched") that there is no time for it to crystallise as it
solidifies, thus leaving the alloy in a glass-like amorphous state.
Suitable materials include Metglas.RTM. 2714A and like materials.
Permalloy or mumetal or the like may also be used.
The core in the secondary device, where provided, is preferably a
high magnetic permeability core. The relative permeability of this
core is preferably at least 100, even more preferably at least 500,
and most preferably at least 1000, with magnitudes of at least
10,000 or 100,000 being particularly advantageous.
The at least one means for generating an electromagnetic field may
be a coil, for example in the form of a length of wire or a printed
strip, or may be in the form of a conductive plate of appropriate
configuration, or may comprise any appropriate arrangement of
conductors. A preferred material is copper, although other
conductive materials, generally metals, may be used as appropriate.
It is to be understood that the term "coil" is here intended to
encompass any appropriate electrical conductor forming an
electrical circuit through which current may flow and thus generate
an electromagnetic field. In particular, the "coil" need not be
wound about a core or former or the like, but may be a simple or
complex loop or equivalent structure.
Preferably, the charging area of the primary unit is large enough
to accommodate the conductor and/or core of the secondary device in
a plurality of orientations thereof. In a particularly preferred
embodiment, the charging area is large enough to accommodate the
conductor and/or core of the secondary device in any orientation
thereof. In this way, power transfer from the primary unit to the
secondary device may be achieved without having to align the
conductor and/or core of the secondary device in any particular
direction when placing the secondary device on the charging surface
of the primary unit.
The substantially laminar charging surface of the primary unit may
be substantially planar, or may be curved or otherwise configured
to fit into a predetermined space, such as a glove compartment of a
car dashboard or the like. It is particularly preferred that the
means for generating an electromagnetic field does not project or
protrude above or beyond the charging surface.
A key feature of the means for generating an electromagnetic field
in the primary unit is that electromagnetic field lines generated
by the means, measured when the primary unit is effectively in
magnetic isolation (i.e. when no secondary device is present on or
in proximity to the charging surface), are distributed in two
dimensions over the at least one charging area and subtend an angle
of 45.degree. or less to the charging area in proximity thereto
(for example, less than the height or width of the charging area)
and over any quarter length part of the charging area measured in a
direction generally parallel to that of the field lines. The
measurement of the field lines in this connection is to be
understood as a measurement of the field lines when averaged over
the quarter length of the charging area, rather than an
instantaneous point measurement. In some embodiments, the field
lines subtend an angle of 30.degree. or less, and in some
embodiments are substantially parallel to at least a central part
of the charging area in question. This is in stark contrast to
prior art systems, where the field lines tend to be substantially
perpendicular to a surface of a primary unit. By generating
electromagnetic fields that are more or less parallel to or at
least have a significant resolved component parallel to the
charging area, it is possible to control the field so as to cause
angular variations thereof, in or parallel to the plane of the
charging area, that help to avoid any stationary nulls in the
electromagnetic field that would otherwise reduce charging
efficiency in particular orientations of the secondary device on
the charging surface. The direction of the field lines may be
rotated through a complete or partial circle, in one or both
directions. Alternatively, the direction may be caused to "wobble"
or fluctuate, or may be switched between two or more directions. In
more complex configurations, the direction of the field lines may
vary as a Lissajous pattern or the like.
In some embodiments, the field lines may be substantially parallel
to each other over any given charging area, or at least have
resolved components in or parallel to the plane of the charging
area that are substantially parallel to each other at any given
moment in time.
It is to be appreciated that one means for generating an
electromagnetic field may serve to provide a field for more than
one charging area; also that more than one means may serve to
provide a field for just one charging area. In other words, there
need not be a one-to-one correspondence of means for generating
electromagnetic fields and charging areas.
The secondary device may adopt a substantially flat form factor
with a core thickness of 2 mm or less. Using a material such as one
or more amorphous metal sheets, it is possible to have core
thickness down to 1 mm or less for applications where size and
weight is important. See FIG. 7a.
In a preferred embodiment, the primary unit may include a pair of
conductors having adjacent coplanar windings which have mutually
substantially parallel linear sections arranged so as to produce a
substantially uniform electromagnetic field extending generally
parallel to or subtending an angle of 45.degree. or less to the
plane of the windings but substantially at right angles to the
parallel sections.
The windings in this embodiment may be formed in a generally spiral
shape, comprising a series of turns having substantially parallel
straight sections.
Advantageously, the primary unit may include first and second pairs
of conductors which are superimposed in substantially parallel
planes with the substantially parallel linear sections of the first
pair arranged generally at right angles to the substantially
parallel linear sections of the second pair, and further comprising
a driving circuit which is arranged to drive them in such a way as
to generate a resultant field which rotates in a plane
substantially parallel to the planes of the windings.
According to a fifth aspect of the present invention, there is
provided a system for transferring power in a contact-less manner
consisting of: a primary unit consisting of at least one electrical
coil whereby each coil features at least one active area whereby
two or more conductors are substantially distributed over this area
in such a fashion that it is possible for a secondary device to be
placed in proximity to a part of this active area where the net
instantaneous current flow in a particular direction is
substantially non-zero; at least one secondary device consisting of
conductors wound around a high permeability core in such a fashion
that it is possible for it to be placed in proximity to an area of
the surface of the primary unit where the net instantaneous current
flow is substantially non-zero; whereby the at least one secondary
device is capable of receiving power by means of electromagnetic
induction when the central axis of the winding is in proximity to
the active area of the primary unit, is substantially not
perpendicular to the plane of the active area of primary unit and
is substantially not parallel to the conductors in the active area
of at least one of the coils of the primary unit.
Where the secondary device comprises an inductively rechargeable
battery or cell, the battery or cell may have a primary axis and be
capable of being recharged by an alternating field flowing in the
primary axis of the battery or cell, the battery or cell consisting
of: an enclosure and external electrical connections similar in
dimensions to industry-standard batteries or cells an
energy-storage means an optional flux-concentrating means a
power-receiving means a means of converting the received power to a
form suitable for delivery to outside the cell through the external
electrical connections, or to recharge the energy storage means, or
both.
The proposed invention is a significant departure from the design
of conventional inductive power transfer systems. The difference
between conventional systems and the proposed system is best
illustrated by looking at their respective magnetic flux line
patterns. (See FIGS. 2a and 4) Conventional System: In a
conventional system (See FIG. 2a), there is typically a planar
primary coil which generates a magnetic field with flux lines
coming out of the plane in a perpendicular fashion. The secondary
device has typically a round or square coil that encircles some or
all of these flux lines. Proposed system: In the proposed system,
the magnetic field travels substantially horizontally across the
surface of the plane (see FIG. 4) instead of directly out of the
plane as illustrated in FIG. 2a. The secondary device hence may
have an elongated winding wound around a magnetic core. See FIGS.
7a and 7b. When the secondary device is placed on the primary unit,
the flux lines would be attracted to travel through the magnetic
core of the secondary device because it is the lowest reluctance
path. This causes the secondary device and the primary unit to be
coupled effectively. The secondary core and winding may be
substantially flattened to form a very thin component.
In describing the invention, specific terminology will be resorted
to for the sake of clarity. However, it is not intended that the
invention be limited to the specific terms so selected and it is to
be understood that each specific term includes all technical
equivalents which operate in a similar manner to accomplish a
similar purpose.
It is to be understood that the term "charging area" used in this
patent application may refer to the area of the at least one means
for generating a field (e.g. one or more conductors in the form of
a coil) or an area formed by a combination of primary conductors
where the secondary device can couple flux effectively. Some
embodiments of this are shown in FIGS. 6a to 6l and 9c as component
740. A feature of a "charging area" is a distribution of conductors
over a significant area of the primary unit configured such that it
is possible for the at least one means for generating a field to be
driven to achieve an instantaneous net flow of flux in one
direction. A primary unit may have more than one charging area. One
charging area is distinct from another charging area when flux
cannot be effectively coupled by the secondary device (such as
those shown in FIG. 7a) in any rotation at the boundary.
It is to be understood that the term "coil" used in this patent
refers to all conductor configurations which feature a charging
area as described above. This includes windings of wire or printed
tracks or a plane as shown in FIG. 8e. The conductors may be made
of copper, gold, alloys or any other appropriate material.
The present application refers to the rotation of a secondary
device in several places. It is to be clarified here that if a
secondary device is rotated, the axis of rotation being referred to
is the one perpendicular to the plane of the charging area.
This radical change in design overcomes a number of drawbacks of
conventional systems. The benefits of the proposed invention
include: No need for accurate alignment: The secondary device can
be placed anywhere on a charging area of the primary unit; Uniform
coupling: In the proposed invention, the coupling between the
primary unit and secondary device is much more uniform over the
charging area compared to a conventional primary and secondary
coil. In a conventional large coil system (see FIG. 2a), the field
strength dips to a minimum at the centre of the coil, in the plane
of the coil (see FIG. 2b). This implies that if sufficient power is
to be effectively transferred at the centre, the field strength at
the minimum has to be above a certain threshold. The field strength
at the maximum will then be excessively higher than the required
threshold and this may cause undesirable effects. Universality: a
number of different secondary devices, even those having different
power requirements, can be placed within charging areas on the
charging surface of the primary unit to receive power
simultaneously; Increased coupling coefficiency: Optional high
permeability magnetic material present in the secondary device
increases the induced flux significantly by offering a low
reluctance path. This can significantly increase the power
transfer. Desirable form factor for secondary device: The geometry
of the system allows thin sheets of magnetic material (such as
amorphous metal ribbons) to be used. This means that secondary
devices can have the form factor of a thin sheet, making it
suitable to be incorporated at the back of mobile phones and other
electronic devices. If magnetic material was to be used in the
centre of conventional coils, it is likely to increase the
bulkiness of the secondary device. Minimised field leakage: When
one or more secondary devices are present in the charging area of
the primary unit, it is possible to use magnetic material in such a
way that more than half of the magnetic circuit is low reluctance
magnetic material (see FIG. 4d). This means that more flux flows
for a given magneto-motive force (mmf). As the induced voltage is
proportional to the rate of change of flux linked, this will
increase the power transfer to the secondary device. The fewer and
shorter the air gaps are in the magnetic circuit, the less the
field will fringe, the closer the flux is kept to the surface of
the primary unit and hence leakage is minimized. Cost
effectiveness: Unlike the multiple-coil design, this solution
requires a much simpler control system and fewer components. Free
axial rotation of secondary device: If the secondary device is thin
or optionally even cylindrical (see FIG. 10), it may be constructed
such that it continues to couple well to the flux regardless of its
rotation about its longest axis. This may in particular be an
advantage if the secondary device is a battery cell fitted within
another device, when its axial rotation may be difficult to
control. The magnetic core in the secondary device may be located
near other parallel planes of metal within or near the device, for
example a copper printed circuit board or aluminium cover. In this
case, the performance of embodiments of the present invention is
significantly better than that of a conventional core-wound coil
because the field lines through a conventional device coil will
suffer flux-exclusion if the coil is placed up against the metal
plane (because the lines of flux must travel perpendicular to the
plane of the coil). Since in embodiments of the present invention
the lines of flux travel along the plane of the core, and therefore
also of the metal plane, performance is improved. An additional
benefit is that the magnetic core in a secondary device of
embodiments of the present invention can act as a shield between
the electromagnetic field generated by the primary unit and any
items (e.g. electrical circuits, battery cells) on the other side
of the magnetic core. Because its permeability is higher than that
of air, the magnetic core of the secondary device of embodiments of
the present invention acts to concentrate magnetic flux, thus
capturing more flux than would otherwise flow through an equivalent
cross-section of air. The size of the core's "shape factor" (the
equivalent flux-capturing sphere) is determined to a first-order
approximation by the longest planar dimension of the core.
Therefore if the core of the secondary device of embodiments of the
present invention has planar dimensions with a significantly
non-square aspect ratio, for example a 4:1 rectangle instead of a
1:1 square, it will capture proportionally more of any flux
travelling parallel to the direction of its longest planar
dimension. Therefore if used in devices which have a constrained
aspect ratio (for example a long thin device such as a headset or
pen), a significant increase in performance will be experienced
compared with that of a conventional coil of the same area.
The primary unit typically consists of the following components.
(See FIG. 5) Power supply: This power supply converts mains voltage
into a lower voltage dc supply. This is typically a conventional
transformer or a switch-mode power supply; Control unit: The
control unit serves the function of maintaining the resonance of
the circuit given that the inductance of the means for generating a
field changes with the presence of secondary devices. To enable
this function, the control unit may be coupled to a sensing unit
which feeds back the current status of the circuit. It may also be
coupled to a library of capacitors which may be switched in and out
as required. If the means for generating a field requires more than
one driving circuit, the control unit may also coordinate the
parameters such as the phase difference or on/off times of
different driving circuits such that the desired effect is
achieved. It is also possible for the Q (quality factor) of the
system to be designed to function over a range of inductances such
that a need for the above control system is eliminated; Driving
circuit: The driving unit is controlled by the control unit and
drives a changing current through the means for generating a field
or a component of the means. More than one driving circuit may be
present depending on the number of independent components in the
means; Means for generating an electromagnetic field: The means
uses current supplied from the driving circuits to generate
electromagnetic fields of pre-defined shapes and intensities. The
exact configuration of the means defines the shape and intensity of
the field generated. The means may include magnetic material to act
as flux guides and also one or more independently driven components
(windings), together forming the charging area. A number of
embodiment designs are possible and examples are shown in FIG. 6.
Sensing unit: The sensing unit retrieves and sends relevant data to
the control unit for interpretation.
The secondary device typically consists of the following
components, as shown in FIG. 5. Magnetic unit: the magnetic unit
converts the energy stored in the magnetic field generated by the
primary unit back into electrical energy. This is typically
implemented by means of a winding wound around a highly permeable
magnetic core. The largest dimension of the core typically
coincides with the central axis of the winding. Conversion unit:
the conversion unit converts the fluctuating current received from
the magnetic unit into a form that is useful to the device that it
is coupled to. For example, the conversion unit may convert the
fluctuating current into an unregulated dc supply by means of a
full-wave bridge rectifier and smoothing capacitor. In other cases,
the conversion unit may be coupled to a heating element or a
battery charger. There is also typically a capacitor present either
in parallel or in series with the magnetic unit to form a resonant
circuit at the operating frequency of the primary unit.
In typical operation, one or more secondary devices are placed on
top of the charging surface of the primary unit. The flux flows
through the at least one conductor and/or core of the secondary
devices present and current is induced. Depending on the
configuration of the means for generating a field in the primary
unit, the rotational orientation of the secondary device may affect
the amount of flux coupled.
The Primary Unit
The primary unit may exist in many different forms, for example: As
a flat platform or pad which can sit on top of tables and other
flat surfaces; Built in to furniture such as desks, tables,
counters, chairs, bookcases etc. such that the primary unit may not
be visible; As part of an enclosure such as a drawer, a box, a
glove compartment of a car, a container for power tools; As a flat
platform or pad which can be attached to a wall and used
vertically.
The primary unit may be powered from different sources, for
example: A mains AC power outlet A vehicle lighter socket Batteries
Fuel Cells Solar Panel Human power
The primary unit may be small enough such that only one secondary
device may be accommodated on the charging surface in a single
charging area, or may be large enough to accommodate many secondary
devices simultaneously, sometimes in different charging areas.
The means for generating a field in the primary unit may be driven
at mains frequency (50 Hz or 60 Hz) or at some higher
frequency.
The sensing unit of the primary unit may sense the presence of
secondary devices, the number of secondary devices present and even
the presence of other magnetic material which is not part of a
secondary device. This information may be used to control the
current being delivered to the field generating means of the
primary unit.
The primary unit and/or the secondary device may be substantially
waterproof or explosion proof.
The primary unit and/or the secondary device may be hermetically
sealed to standards such as IP66.
The primary unit may incorporate visual indicators (for example,
but not limited to, light emitting devices, such as light emitting
diodes, electrophosphorescent displays, light emitting polymers, or
light reflecting devices, such as liquid crystal displays or MITs
electronic paper) to indicate the current state of the primary
unit, the presence of secondary devices or the number of secondary
devices present or any combination of the above.
The Means for Generating an Electromagnetic Field
The field generating means as referred to in this application
includes all configurations of conductors where: The conductors are
substantially distributed in the plane and; Substantial areas of
the plane exist where there is a non-zero net instantaneous current
flow. These are areas on which, given the correct orientation, the
secondary devices will couple effectively and receive power. (See
FIG. 6) The conductors are capable of generating an electromagnetic
field where the field lines subtend an angle of 45.degree. or less
or are substantially parallel to a substantial area of the
plane.
FIG. 6 illustrate some possibilities for such a primary conductor.
Although most of the configurations are in fact coil windings, it
is to be appreciated that the same effect can also be achieved with
conductor planes which are not typically considered to be coils
(See FIG. 6e). These drawings are typical examples and are
non-exhaustive. These conductors or coils may be used in
combination such that the secondary device can couple effectively
in all rotations whilst on the charging area(s) of the primary
unit.
Magnetic Material
It is possible to use magnetic materials in the primary unit to
enhance performance. Magnetic material may be placed below one or
more charging areas or the entire charging surface such that there
is also a low reluctance path on the underside of the conductors
for the flux to complete its path. According to theory, an analogy
can be drawn between magnetic circuits and electrical circuits.
Voltage is analogous to magneto-motive force (mmf), resistance is
analogous to reluctance and current is analogous to flux. From
this, it can be seen that for a given mmf, flux flow will increase
if the reluctance of the path is decreased. By providing magnetic
material to the underside of the charging area, the reluctance of
the magnetic circuit is essentially decreased. This substantially
increases the flux linked by the secondary device and ultimately
increases the power transferred. FIG. 4d illustrates a sheet of
magnetic material placed underneath the charging area and the
resulting magnetic circuit. Magnetic material may also be placed
above the charging surface and/or charging area(s) and below the
secondary devices to act as a flux guide. This flux guide performs
two functions: Firstly, the reluctance of the whole magnetic
circuit is further decreased allowing more flux to flow. Secondly,
it provides a low reluctance path along the top surface of the
charging area(s) so the flux lines will flow through these flux
guides in favour of flowing through the air. Hence this has the
effect of containing the field close to the charging surface of the
primary unit instead of in the air. The magnetic material used for
flux guides may be strategically or deliberately chosen to have
different magnetic properties to the magnetic core (where provided)
of the secondary device. For example, a material with lower
permeability and higher saturation may be chosen. High saturation
means that the material can carry more flux and the lower
permeability means that when a secondary device is in proximity, a
significant amount of flux would then choose to travel through the
secondary device in favour of the flux guide. (See FIG. 8) In some
configurations of the primary unit field generating means, there
may be conductors present that do not form part of the charging
area, such as the component marked 745 in FIGS. 6a and 6b. In such
cases, one may wish to use magnetic material to shield the effects
of these conductors. Examples of some materials which may be used
include but are not limited to: amorphous metal (metallic glass
alloys such as MetGlas.TM.), mesh of wires made of magnetic
material, steel, ferrite cores, mumetal and permalloy. The
Secondary Device
The secondary device may take a variety of shapes and forms.
Generally, in order for good flux linkage, a central axis of the
conductor (for example, a coil winding) should be substantially
non-perpendicular to the charging area(s). The secondary device may
be in the shape of a flattened winding. (See FIG. 7a) The magnetic
core inside can consist of sheets of magnetic material such as
amorphous metals. This geometry allows the secondary device to be
incorporated at the back of electronic devices such as mobile
phones, personal digital assistants and laptops without adding bulk
to the device. The secondary device may be in the shape of a long
cylinder. A long cylindrical core could be wound with conductors
(See FIG. 7b). The secondary device may be an object with magnetic
material wrapped around it. An example is a standard-sized (AA,
AAA, C, D) or other sized/shaped (e.g. dedicated/customised for
particular applications) rechargeable battery cell with for example
magnetic material wrapped around the cylinder and windings around
the cylindrical body. The secondary device may be a combination of
two or more of the above. The above embodiments may even be
combined with a conventional coil.
The following non-exhaustive list illustrates some examples of
objects that can be coupled to a secondary device to receive power.
Possibilities are not limited to those described below: A mobile
communication device, for example a radio, mobile telephone or
walkie-talkie; A portable computing device, for example a personal
digital assistant or palmtop or laptop computer; Portable
entertainment devices, for example a music player, games console or
toy; Personal care items, for example a toothbrush, shaver, hair
curler, hair rollers; A portable imaging device, for example a
video camcorder or a camera; Containers of contents that may
require heating, for example coffee mugs, plates, cooking pots,
nail-polish and cosmetic containers; Consumer devices, for example
torches, clocks and fans; Power tools, for example cordless drills
and screwdrivers; Wireless peripheral devices, for example wireless
computer mouse, keyboard and headset; Time keeping devices, for
example clock, wrist watch, stop watch and alarm clock; A
battery-pack for insertion into any of the above; A standard-sized
battery cell.
In the case of unintelligent secondary devices such as a battery
cell, some sophisticated charge-control means may also be necessary
to meter inductive power to the cell and to deal with situations
where multiple cells in a device have different charge states.
Furthermore, it becomes more important for the primary unit to be
able to indicate a "charged" condition, since the secondary cell or
battery may not be easily visible when located inside another
electrical device.
A possible system comprising an inductively rechargeable battery or
cell and a primary unit is shown in FIG. 10. In addition to the
freedom to place the battery 920 freely in (X, Y) and optionally
rotate it in rZ, relative to the primary unit 910, the battery can
also be rotated along its axis rA while continuing to receive
power.
When a user inserts a battery into a portable device, it is not
easy to ensure that it has any given axial rotation. Therefore,
embodiments of the present invention are highly advantageous
because they can ensure that the battery can receive power while in
any random orientation about rA.
The battery or cell may include a flux concentrating means that may
be arranged in a variety of ways: 1. As shown in FIG. 11a, a cell
930 may be wrapped in a cylinder of flux-concentrating material
931, around which is wrapped a coil of wire 932. a. The cylinder
may be long or short relative to the length of the cell. 2. As
shown in FIG. 11b, a cell 930 may have a portion of
flux-concentrating material 931 on its surface, around which is
wrapped a coil of wire 932. a. The portion may be conformed to the
surface of the cell, or embedded within it. b. Its area may be
large or small relative to the circumference of the cell, and long
or short relative to the length of the cell. 3. As shown in FIG.
11c, a cell 930 may contain a portion of flux-concentrating
material 931 within it, around which is wrapped a coil of wire 932.
a. The portion may be substantially flat, cylindrical, rod-like, or
any other shape. b. Its width may be large or small relative to the
diameter of the cell c. Its length may be large or small relative
to the length of the cell
In any of these cases, the flux-concentrator may be a functional
part of the battery enclosure (for example, an outer zinc
electrode) or the battery itself (for example, an inner
electrode).
Issues relating to charging of secondary cells (e.g. AA
rechargeable cells in-situ within an appliance include: Terminal
voltage could be higher than normal. Cells in series may behave
strangely, particularly in situations where some cells are charged,
others not. Having to provide enough power to run the device and
charge the cell. If fast-charging is effected incorrectly, the
cells may be damaged.
Accordingly, some sophisticated charge-control means to meter
inductive power to the appliance and the cell is advantageously
provided. Furthermore, it becomes more important for the primary
unit to be able to indicate a "charged" condition, since the
secondary cell or battery may not be easily visible when located
inside an electrical device.
A cell or battery enabled in this fashion may be charged whilst
fitted in another device, by placing the device onto the primary
unit, or whilst outside the device by placing the cell or battery
directly onto the primary unit.
Batteries enabled in this fashion may be arranged in packs of cells
as in typical devices (e.g. end-to-end or side-by-side), allowing a
single pack to replace a set of cells.
Alternatively, the secondary device may consist of a flat "adapter"
which fits over the batteries in a device, with thin electrodes
which force down between the battery electrodes and the device
contacts.
Rotating Electromagnetic Field
In the coils such as those in FIGS. 6, 9a and 9b, the secondary
devices will generally only couple effectively when the windings
are placed substantially parallel to the direction of net current
flow in the primary conductor as shown by the arrow 1. In some
applications, one might require a primary unit which will transfer
power effectively to secondary devices regardless of their rotation
as long as: the central axis of the secondary conductor is not
perpendicular to the plane and; the secondary device is in close
proximity to the primary unit
To enable this, it is possible to have two coils, for example one
positioned on top of the other or one woven into or otherwise
associated with the other, the second coil capable of generating a
net current flow substantially perpendicular to the direction of
the first coil at any point in the active area of the primary unit.
These two coils may be driven alternately such that each is
activated for a certain period of time. Another possibility is to
drive the two coils in quadrature such that a rotating magnetic
dipole is generated in the plane. This is illustrated in FIG. 9.
This is also possible with other combinations of coil
configurations.
Resonant Circuits
It is known in the art to drive coils using parallel or series
resonant circuits. In series resonant circuits for example, the
impedance of the coil and the capacitor are equal and opposite at
resonance, hence the total impedance of the circuit is minimised
and a maximum current flows through the primary coil. The secondary
device is typically also tuned to the operating frequency to
maximise the induced voltage or current.
In some systems like the electric toothbrush, it is common to have
a circuit which is detuned when the secondary device is not present
and tuned when the secondary device is in place. The magnetic
material present in the secondary device shifts the self-inductance
of the primary unit and brings the circuit into resonance. In other
systems like passive radio tags, there is no magnetic material in
the secondary device and hence does not affect the resonant
frequency of the system. These tags are also typically small and
used far from the primary unit such that even if magnetic material
is present, the inductance of the primary is not significantly
changed.
In the proposed system, this is not the case: High permeability
magnetic material may be present in the secondary device and is
used in close proximity to the primary unit; One or more secondary
devices may be brought in close proximity to the primary unit
simultaneously.
This has the effect of shifting the inductance of the primary
significantly and also to different levels depending on the number
of secondary devices present on the pad. When the inductance of the
primary unit is shifted, the capacitance required for the circuit
to resonant at a particular frequency also changes. There are three
methods for keeping the circuit at resonance: By means of a control
system to dynamically change the operating frequency; By means of a
control system to dynamically change the capacitance such that
resonance is achieved at the predefined frequency; By means of a
low Q system where the system remains in resonance over a range of
inductances.
The problem with changing the operating frequency is that the
secondary devices are typically configured to resonate at a
predefined frequency. If the operating frequency changes, the
secondary device would be detuned. To overcome this problem, it is
possible to change the capacitance instead of the operating
frequency. The secondary devices can be designed such that each
additional device placed in proximity to the primary unit will
shift the inductance to a quantised level such that an appropriate
capacitor can be switched in to make the circuit resonate at a
predetermined frequency. Because of this shift in resonant
frequency, the number of devices on the charging surface can be
detected and the primary unit can also sense when something is
brought near or taken away from the charging surface. If a
magnetically permeable object other than a valid secondary device
is placed in the vicinity of the charging surface, it is unlikely
to shift the system to the predefined quantised level. In such
circumstances, the system could automatically detune and reduce the
current flowing into the coil.
For a better understanding of the present invention and to show how
it may be carried into effect, reference shall now be made, by way
of example only, to the accompanying drawings, in which:
FIG. 1 shows the magnetic design of typical prior art contact-less
power transfer systems which require accurate alignment of the
primary unit and secondary device;
FIG. 2a shows the magnetic design of another typical prior art
contact-less power transfer system which involves a large coil in
the primary unit;
FIG. 2b shows the non-uniform field distribution inside the large
coil at 5 mm distance from the plane of the coil, exhibiting a
minimum in the centre;
FIG. 3 shows a multiple-coil system where each coil is
independently driven such that a localised field can be
generated.
FIG. 4a shows an embodiment of the proposed system which
demonstrates a substantial departure from prior art with no
secondary devices present;
FIG. 4b shows an embodiment of the proposed system with two
secondary devices present;
FIG. 4c shows a cross section of the active area of the primary
unit and the contour lines of the magnetic flux density generated
by the conductors.
FIG. 4d shows the magnetic circuit for this particular embodiment
of the proposed invention;
FIG. 5 shows a schematic drawing of an embodiment of the primary
unit and the secondary device;
FIGS. 6a to 6l show some alternative embodiment designs for the
field generating means or a component of the field generating means
of the primary unit;
FIGS. 7a and 7b show some possible designs for the magnetic unit of
the secondary device;
FIGS. 8a 8f show the effect of flux guides (the thickness of the
flux guide has been exaggerated for clarity);
FIG. 8a shows that without flux guides, the field tends to fringe
into the air directly above the active area;
FIG. 8b shows the direction of current flow in the conductors in
this particular embodiment;
FIG. 8c shows that the flux is contained within the flux guides
when magnetic material is placed on top of the charging area;
FIG. 8d shows a secondary device on top of the primary unit;
FIG. 8e shows a cross section of the primary unit without any
secondary devices;
FIG. 8f shows a cross section of the primary unit with a secondary
device on top and demonstrates the effect of using a secondary core
with higher permeability than the flux guide.
FIG. 9a shows a particular coil arrangement with a net
instantaneous current flow shown by the direction of the arrow;
FIG. 9b shows a similar coil arrangement to FIG. 9a except rotated
by 90 degrees;
FIG. 9c shows the charging area of the primary unit if the coil of
FIG. 9a is placed on top of FIG. 9b. If the coil in FIG. 9a if
driven in quadrature to FIG. 9b, the effect is a rotating magnetic
dipole shown here;
FIG. 10 shows the case where the secondary device has an axial
degree of rotation;
FIG. 11 shows various arrangements of secondary devices with axial
degrees of rotation;
FIG. 12a and FIG. 12b show another embodiment of the type of coil
arrangement shown in FIG. 9a and FIG. 9b; and
FIG. 13 shows a simple embodiment of driving unit electronics.
Referring firstly to FIG. 1, there is shown two examples of prior
art contact-less power transfer systems which both require accurate
alignment of a primary unit and a secondary device. This embodiment
is typically used in electric toothbrush or mobile phone
chargers.
FIG. 1a shows a primary magnetic unit 100 and a secondary magnetic
unit 200. On the primary side, a coil 110 is wound around a
magnetic core 120 such as ferrite. Similarly, the secondary side
consists of a coil 210 wound around another magnetic core 220. In
operation, an alternating current flows in to the primary coil 110
and generates lines of flux 1. When a secondary magnetic unit 200
is placed such that it is axially aligned with the primary magnetic
unit 100, the flux 1 will couple from the primary into the
secondary, inducing a voltage across the secondary coil 210.
FIG. 1b shows a split transformer. The primary magnetic unit 300
consists of a U-shaped core 320 with a coil 310 wound around it.
When alternating current flows into the primary coil 310, changing
lines of flux are generated 1. The secondary magnetic unit 400
consists of a second U-shaped core 420 with another coil 410 wound
around it. When the secondary magnetic unit 400 is placed on the
primary magnetic unit 300 such that the arms of the two U-shaped
cores are in alignment, the flux will couple effectively into the
core of the secondary 420 and induce voltage across the secondary
coil 410.
FIG. 2a is another embodiment of prior art inductive systems
typically used in powering radio frequency passive tags. The
primary typically consists of a coil 510 covering a large area.
Multiple secondary devices 520 will have voltage induced therein
when they are within the area encircled by the primary coil 510.
This system does not require the secondary coil 520 to be
accurately aligned with the primary coil 510. FIG. 2b shows a graph
of the magnitude of magnetic flux intensity across the area
encircled by the primary coil 510 at 5 mm above the plane of the
primary coil. It shows a non-uniform field, which exhibits a
minimum 530 at the centre of the primary coil 510.
FIG. 3 is another embodiment of a prior art inductive system
wherein a multiple coil array is used. The primary magnetic unit
600 consists of an array of coils including coils 611, 612, 613.
The secondary magnetic unit 700 may consist of a coil 710. When the
secondary magnetic unit 700 is in proximity to some coils in the
primary magnetic unit 600, the coils 611, 612 are activated while
other coils such as 613 remain inactive. The activated coils 611,
612 generate flux, some of which will couple into the secondary
magnetic unit 700.
FIG. 4 shows an embodiment of the proposed invention. FIG. 4a shows
a primary coil 710 wound or printed in such a fashion that there is
a net instantaneous current flow within the active area 740. For
example, if a dc current flows through the primary coil 710, the
conductors in the active area 740 would all have current flowing in
the same direction. Current flowing through the primary coil 710
generates flux 1. A layer of magnetic material 730 is present
beneath the charging area to provide a return path for the flux.
FIG. 4b shows the same primary magnetic unit as shown in FIG. 4a
with two secondary devices 800 present. When the secondary devices
800 are placed in the correct orientation on top of the charging
area 740 of the primary magnetic unit, the flux 1 will flow through
the magnetic core of the secondary devices 800 instead of flowing
through the air. The flux 1 flowing through the secondary core
would hence induce current in the secondary coil.
FIG. 4c shows some contour lines for the flux density of the
magnetic field generated by the conductors 711 in the charging area
740 of the primary magnetic unit. There is a layer of magnetic
material 730 beneath the conductors to provide a low reluctance
return path for the flux.
FIG. 4d shows a cross-section of the charging area 740 of the
primary magnetic unit. A possible path for the magnetic circuit is
shown. The magnetic material 730 provides a low reluctance path for
the circuit and also the magnetic core 820 of the secondary
magnetic device 800 also provides a low reluctance path. This
minimizes the distance the flux has to travel through the air and
hence minimizes leakage.
FIG. 5 shows a schematic drawing of an embodiment of the whole
system of the proposed invention. In this embodiment, the primary
unit consists of a power supply 760, a control unit 770, a sensing
unit 780 and an electromagnetic unit 700. The power supply 760
converts the mains (or other sources of power) into a dc supply at
an appropriate voltage for the system. The control unit 770
controls the driving unit 790 which drives the magnetic unit 700.
In this embodiment, the magnetic unit consists of two independently
driven components, coil 1 and coil 2, arranged such that the
conductors in the charging area of coil 1 would be perpendicular to
the conductors in the charging area of coil 2. When the primary
unit is activated, the control unit causes a 90-degree phase shift
between the alternating current that flows through coil 1 and coil
2. This creates a rotating magnetic dipole on the surface of the
primary magnetic unit 700 such that a secondary device is able to
receive power regardless of its rotational orientation (See FIG.
9). In standby mode where no secondary devices are present, the
primary unit is detuned and current flow into the magnetic unit 700
is minimised. When a secondary device is placed on top of the
charging area of the primary unit, the inductance of the primary
magnetic unit 700 is changed. This brings the primary circuit into
resonance and the current flow is maximised. When there are two
secondary devices present on the primary unit, the inductance is
changed to yet another level and the primary circuit is again
detuned. At this point, the control unit 770 uses feedback from the
sensing unit 780 to switch another capacitor into the circuit such
that it is tuned again and current flow is maximised. In this
embodiment, the secondary devices are of a standard size and a
maximum of six standard-sized devices can receive power from the
primary unit simultaneously. Due to the standard sizes of the
secondary devices, the change in inductance due to the change in
secondary devices in proximity is quantized to a number of
predefined levels such that only a maximum of 6 capacitances is
required to keep the system operating at resonance.
FIGS. 6a to 6l show a number of different embodiments for the coil
component of the primary magnetic unit. These embodiments may be
implemented as the only coil component of the primary magnetic
unit, in which case the rotation of the secondary device is
important to the power transfer. These embodiments may also be
implemented in combination, not excluding embodiments which are not
illustrated here. For example, two coils illustrated in FIG. 6a may
be placed at 90 degrees to each other to form a single magnetic
unit. In FIGS. 6a to 6e, the charging area 740 consists of a series
of conductors with net current generally flowing in the same
direction. In certain configurations, such as FIG. 6c, there is no
substantial linkage when the secondary device is placed directly
over the centre of the coil and hence power is not transferred. In
FIG. 6d, there is no substantial linkage when the secondary device
is positioned in the gap between the two charging areas 740.
FIG. 6f shows a specific coil configuration for the primary unit
adapted to generate electromagnetic field lines substantially
parallel to a surface of the primary unit within the charging area
740. Two primary windings 710, one on either side of the charging
area 740, are formed about opposing arms of a generally rectangular
flux guide 750 made out of a magnetic material, the primary
windings 710 generating opposing electromagnetic fields. The flux
guide 750 contains the electromagnetic fields and creates a
magnetic dipole across the charging area 740 in the direction of
the arrows indicated on the Figure. When a secondary device is
placed in the charging area 740 in a predetermined orientation, a
low reluctance path is created and flux flows through the secondary
device, causing effective coupling and power transfer. It is to be
appreciated that the flux guide 750 need not be continuous, and may
in fact be formed as two opposed and non-linked horseshoe
components.
FIG. 6g shows another possible coil configuration for the primary
unit, the coil configuration being adapted to generate
electromagnetic field lines substantially parallel to the charging
surface of the primary unit within the charging area 740. A primary
winding 710 is wound around a magnetic core 750 which may be
ferrite or some other suitable material. The charging area 740
includes a series of conductors with instantaneous net current
generally flowing in the same direction. The coil configuration of
FIG. 6g is in fact capable of supporting or defining a charging
area 740 on both upper and lower faces as shown in the drawing, and
depending on the design of the primary unit, one or both of the
charging areas may be made available to secondary devices.
FIG. 6h shows a variation of the configuration of FIG. 6g. Instead
of the primary windings 710 being evenly spaced as in FIG. 6g, the
windings 710 are not evenly spaced. The spacing and variations
therein can be selected or designed so as to provide improved
uniformity of performance or field strength levels over the
charging area 740.
FIG. 6i shows an embodiment in which two primary windings 710 as
shown in FIG. 6g are located in a mutually orthogonal configuration
so as to enable a direction of the field lines to be dynamically
switched or rotated to other orientations about the plane of the
charging surface.
FIGS. 6j and 6k show additional two-coil configurations for the
primary unit which are not simple geometric shapes with
substantially parallel conductors.
In FIG. 6j, line 710 indicates one of a set of current-carrying
conductors lying in the plane of the charging surface 600. The
shape of the main conductor 710 is arbitrary and need not be a
regular geometric figure--indeed, conductor 710 may have straight
and curved sections and may intersect with itself. One or more
subsidiary conductors 719 are arranged alongside and generally
parallel (at any given local point) to the main conductor 710 (only
two subsidiary conductors 719 are shown here for clarity). Current
flow in subsidiary conductors 719 will be in the same direction as
in the main conductor 710. The subsidiary conductors 719 may be
connected in series or parallel so as to form a single coil
arrangement.
In FIG. 6k, a set of current-carrying conductors 720 (only some of
which are shown for clarity) is arranged in the plane of the
charging surface 600. A main conductor 710 is provided as in FIG.
6j, and the conductors 720 are each arranged so as to be locally
orthogonal to the main conductor 710. The conductors 720 may be
connected in series or parallel so as to form a single coil
arrangement. If a first sinusoidal current is fed into the
conductor 710, and a second sinusoidal current having a 90.degree.
phase shift relative to the first current is fed into the coil 720,
then by varying the relative proportions and signs of the two
currents a direction of a resultant electromagnetic field vector at
most points on the charging area 740 will be seen to rotate through
360.degree..
FIG. 6l shows yet another alternative arrangement in which the
magnetic core 750 is in the shape of a round disc with a hole in
the centre. The first set of current carrying conductors 710 is
arranged in a spiral shape on the surface of the round disc. The
second set of conductors 720 is wound in a toroidal format through
the centre of the disc and out to the perimeter in a radial
fashion. These conductors can be driven in such a way, for example
with sinusoidal currents at quadrature, that when a secondary
device is placed at any point inside the charging area 740 and
rotated about an axis perpendicular to the charging area, no nulls
are observed by the secondary device.
FIGS. 7a and 7b are embodiments of the proposed secondary devices.
A winding 810 is wound around a magnetic core 820. Two of these may
be combined in a single secondary device, at right angles for
example, such that the secondary device is able to effectively
couple with the primary unit at all rotations. These may also be
combined with standard coils, as the ones shown in FIG. 2a 520 to
eliminate dead spots.
FIGS. 8a 8f show the effect of flux guides 750 positioned on top of
the charging area. The thickness of the material has been
exaggerated for the sake of clarity but in reality would be in the
order of millimeters thick. The flux guides 750 will minimize
leakage and contain the flux at the expense of reducing the amount
of flux coupled to the secondary device. In FIG. 8a, a primary
magnetic unit is shown without flux guides 750. The field will tend
to fringe into the air directly above the charging area. With flux
guides 750, as shown in FIG. 8b to 8f, the flux is contained within
the plane of the material and leakage is minimised. In FIG. 8e,
when there is no secondary device 800 on top, the flux remains in
the flux guide 750. In FIG. 8f, when a secondary device 800 is
present with a relatively more permeable material as the core, part
of the flux will flow via the secondary device. The permeability of
the flux guide 750 can be chosen such that it is higher than that
of typical metals such as steel. When other materials such as
steel, which are not part of secondary devices 800, are placed on
top, most of the flux will remain in the flux guide 750 instead of
travelling through the object. The flux guide 750 may not be a
continuous layer of magnetic material but may have small air gaps
in them to encourage more flux flow into the secondary device 800
when it is present.
FIG. 9 shows an embodiment of a primary unit whereby more than one
coil is used. FIG. 9a shows a coil 710 with a charging area 740
with current flow parallel to the direction of the arrow 2. FIG. 9b
shows a similar coil arranged at 90 degrees to the one in FIG. 9a.
When these two coils are placed on top of each other such that the
charging area 740 overlaps, the charging area will look like the
illustration in FIG. 9c. Such an embodiment would allow the
secondary device to be at any rotation on top of the primary unit
and couple effectively.
FIG. 10 shows an embodiment where the secondary device has an axial
degree of rotation, for example where it is, or is embedded within,
a battery cell. In this embodiment the secondary device may be
constructed such that it couples to the primary flux when in any
axial rotation (rA) relative to the primary unit (910), as well as
having the same degrees of freedom described above (i.e.
translational (X, Y) and optionally rotational perpendicular to the
plane of the primary (rZ)).
FIG. 11a shows one arrangement where a rechargeable battery cell
930 is wrapped with an optional cylinder of flux-concentrating
material 931 which is itself wound with copper wire 932. The
cylinder may be long or short relative to the length of the
cell.
FIG. 11b shows another arrangement where the flux-concentrating
material 931 covers only part of the surface of the cell 930, and
has copper wire 932 wrapped around it (but not the cell). The
material and wire may be conformed to the surface of the cell.
Their area may be large or small relative to the circumference of
the cell, and long or short relative to the length of the cell.
FIG. 11c shows another arrangement where the flux-concentrating
material 931 is embedded within the cell 930 and has copper wire
932 wrapped around it. The material may be substantially flat,
cylindrical, rod-like, or any other shape, its width may be large
or small relative to the diameter of the cell, and its length may
be large or small relative to the length of the cell.
In any case shown in FIGS. 10 and 11, any flux-concentrating
material may also be a functional part of the battery enclosure
(for example, an outer zinc electrode) or the battery itself (for
example, an inner electrode).
In any case shown in FIGS. 10 and 11, the power may be stored in a
smaller standard cell (e.g. AAA size) fitted within the larger
standard cell enclosure (e.g. AA).
FIG. 12 shows an embodiment of a primary unit similar to that shown
in FIG. 9. FIG. 12a shows a coil generating a field in a direction
horizontal to the page, FIG. 12b shows another coil generating a
field vertical to the page, and the two coils would be mounted in a
substantially coplanar fashion, possibly with one above the other,
or even intertwined in some fashion. The wire connections to each
coil are shown 940 and the charging area is represented by the
arrows 941.
FIG. 13 shows a simple embodiment of the Driving Unit (790 of FIG.
5). In this embodiment there is no Control Unit. The PIC processor
960 generates two 23.8 kHz square waves 90 degrees out of phase
with one another. These are amplified by components 961 and driven
into two coil components 962, which are the same magnetic units
shown in FIG. 12a and FIG. 12b. Although the driving unit is
providing square waves, the high resonant "Q" of the magnetic units
shapes this into a sinusoidal waveform.
The preferred features of the invention are applicable to all
aspects of the invention and may be used in any possible
combination.
Throughout the description and claims of this specification, the
words "comprise" and "contain" and variations of the words, for
example "comprising" and "comprises", mean "including but not
limited to", and are not intended to (and do not) exclude other
components, integers, moieties, additives or steps.
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